Many plotter systems include buffers to temporarily store input data before plotting the data. Many other systems, without buffers, generally plot the data as it is received. In both types of systems, the plot head and pen are generally made to move directly from data point to data point in somewhat jerky, discrete steps when plotting the data. After a data point is plotted, the plot head remains stationary waiting for a subsequent data point. During this stationary period, a disproportionate amount of ink from the pen usually accumulates on the writing surface under the pen, compared to the amount that accumulates on portions of the surface when the pen is in motion. This disproportionate accumulation of ink causes the trace or line segment being plotted to become nonuniform in appearance. Even in plotter systems that provide for a uniform trace when the pen is in motion (i.e., systems that modulate or vary the pressure of ink to the pen as a function of head velocity), appreciable amounts of stationary periods still produce nonuniformity in the trace at the beginning-and end-points of line segments. What is needed, therefore, is a plotter system that also provides for uniformity of trace at the beginning-and end-points of line segments.
Accordingly, as an illustrated preferred embodiment of the present invention, a plotter system is provided having an adaptive velocity means, motor unit and plot head for improving plotted line quality and providing uniformity of trace by substantially reducing the length of each period that the plot head remains stationary waiting for data. The adaptive velocity means includes a RAM, a ROM with a stored routine, and a processor unit for adapting the head velocity to (i.e., for varying the head velocity with) the input data rate and to the distance between data values, to produce substantially smooth (nonjerky), continuous head motion .